1. Field of the Invention
This invention relates generally to engineering modeling and design of water distribution systems, and more particularly, to software tools for estimating the costs associated with such systems.
2. Background Information
Water distribution systems represent an important investment on the part of a water utility, and a critical aspect of the infrastructure of a community. Software used as a tool for the optimal design of a water distribution system allows a company to make intelligent decisions on the investment, new construction, or rehabilitation of a system. The cost of construction, and operation, of a water distribution system is undoubtedly an important factor in planning for the provision of sufficient water supply for a community, not only at the current time, but also over a reasonable future-planning horizon. Software tools can allow an engineer to calculate a planning level estimate of the costs associated with an entire system or a portion of the system. This makes it easier to compare the costs associated with various scenarios, thus helping to ensure that the most cost-effective design and ultimate operation is chosen.
A substantial, non-construction cost in the operation of a water distribution system is that of the electrical energy to be utilized by the system. For example, the cost of operating the pumps during an extended period is an important item of information to be taken into account. This energy is an additional consideration in a cost analysis.
Conventionally, energy cost analyses have not been complete. For example, if an engineer includes a tank in a proposed network that has an initial water tank level for a particular day of ten feet of water and, during the course of the simulation, the water level falls to five feet, then this event translates into an energy loss, because at some point the pump will have to expand energy to refill the tank back to its original level. Conversely, if the water level in a tank at the end of a simulation is greater than the initial level, then that should be taken into account in the cost associated with the refilled tank. In other words, a cost analysis and/or cost estimate should not be based solely on the costs of running a pump, but should include storage considerations.
Up to now, these considerations have not been taken into account in known water distribution network software. For instance, if a pump is off for an extended period simulation in which a tank meets the demand of a network for a twenty-four hour period without requiring additional water, and a cost analysis is run without accounting for storage gains and losses for that twenty-four hour period, then a typical program would calculate the daily energy cost for that network as zero, as if the pumps did not run, and no energy was consumed. This is obviously incorrect, as energy will be required afterwards to refill the tank to account for the usage during the previous day.
Moreover, the energy cost pricing structure of the utility can include a number of different factors. More specifically, there are two parts to the energy cost, a usage charge and a peak demand charge (also known as a ratchet charge). The “usage cost” is a direct cost related to the amount of energy used (e.g., XkWh at Y cents per kWh), where the unit cost per kWh may vary over the course of the day. For example, there may be high rates during the day when usage is higher, and low rates during the night when usage is lower. The “demand charge” is an additional cost which is related to the peak power that is used (power is energy/time), and reflects the need for the electrical utility to provide energy at a certain peak rate to meet a peak demand (even if that peak rate is only needed for a few minutes).
Each utility has its own billing structure for power used, and residential usage rates usually are different than industrial usage rates. Many industrial usage rate structures can be rather complex. And yet, known water distribution network modeling systems do not typically take into account the total energy cost during a particular time based on the relevant rate structure, including the billing cycle.
There remains a need, therefore, for a water distribution network energy cost estimation system, which takes into account storage levels and related considerations.
There remains a further need for a water distribution network cost estimation system, which also includes electrical utility rate structure information and pricing information to be taken into account that is mapped to the relevant time period of the simulation.
It is an object of the present invention to provide a software tool for modeling and designing a water distribution system that incorporates energy cost estimation that includes the cost of energy usage, the cost of refilling of storage tanks, and utility rate structures to provide a more accurate estimate of the energy costs associated with the operation of the system being designed, or operated, and a more accurate basis for comparing the costs associated with one trial solution versus the cost associated with a different proposed trial solution, for example.